package com.clark.io;

import static com.clark.func.Functions.closeQuietly;
import static com.clark.func.Functions.copy;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * An output stream which will retain data in memory until a specified threshold
 * is reached, and only then commit it to disk. If the stream is closed before
 * the threshold is reached, the data will not be written to disk at all.
 * <p>
 * This class originated in FileUpload processing. In this use case, you do not
 * know in advance the size of the file being uploaded. If the file is small you
 * want to store it in memory (for speed), but if the file is large you want to
 * store it to file (to avoid memory issues).
 * 
 * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
 * @author gaxzerow
 * 
 * @version $Id: DeferredFileOutputStream.java 736890 2009-01-23 02:02:22Z
 *          niallp $
 */
public class DeferredFileOutputStream extends ThresholdingOutputStream {

    // ----------------------------------------------------------- Data members

    /**
     * The output stream to which data will be written prior to the theshold
     * being reached.
     */
    private ByteArrayOutputStream memoryOutputStream;

    /**
     * The output stream to which data will be written at any given time. This
     * will always be one of <code>memoryOutputStream</code> or
     * <code>diskOutputStream</code>.
     */
    private OutputStream currentOutputStream;

    /**
     * The file to which output will be directed if the threshold is exceeded.
     */
    private File outputFile;

    /**
     * The temporary file prefix.
     */
    private final String prefix;

    /**
     * The temporary file suffix.
     */
    private final String suffix;

    /**
     * The directory to use for temporary files.
     */
    private final File directory;

    /**
     * True when close() has been called successfully.
     */
    private boolean closed = false;

    // ----------------------------------------------------------- Constructors

    /**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a file beyond that point.
     * 
     * @param threshold
     *            The number of bytes at which to trigger an event.
     * @param outputFile
     *            The file to which data is saved beyond the threshold.
     */
    public DeferredFileOutputStream(int threshold, File outputFile) {
        this(threshold, outputFile, null, null, null);
    }

    /**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a temporary file beyond that point.
     * 
     * @param threshold
     *            The number of bytes at which to trigger an event.
     * @param prefix
     *            Prefix to use for the temporary file.
     * @param suffix
     *            Suffix to use for the temporary file.
     * @param directory
     *            Temporary file directory.
     * 
     * @since Commons IO 1.4
     */
    public DeferredFileOutputStream(int threshold, String prefix,
            String suffix, File directory) {
        this(threshold, null, prefix, suffix, directory);
        if (prefix == null) {
            throw new IllegalArgumentException(
                    "Temporary file prefix is missing");
        }
    }

    /**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data either to a file beyond that point.
     * 
     * @param threshold
     *            The number of bytes at which to trigger an event.
     * @param outputFile
     *            The file to which data is saved beyond the threshold.
     * @param prefix
     *            Prefix to use for the temporary file.
     * @param suffix
     *            Suffix to use for the temporary file.
     * @param directory
     *            Temporary file directory.
     */
    private DeferredFileOutputStream(int threshold, File outputFile,
            String prefix, String suffix, File directory) {
        super(threshold);
        this.outputFile = outputFile;

        memoryOutputStream = new ByteArrayOutputStream();
        currentOutputStream = memoryOutputStream;
        this.prefix = prefix;
        this.suffix = suffix;
        this.directory = directory;
    }

    // --------------------------------------- ThresholdingOutputStream methods

    /**
     * Returns the current output stream. This may be memory based or disk
     * based, depending on the current state with respect to the threshold.
     * 
     * @return The underlying output stream.
     * 
     * @exception IOException
     *                if an error occurs.
     */
    @Override
    protected OutputStream getStream() throws IOException {
        return currentOutputStream;
    }

    /**
     * Switches the underlying output stream from a memory based stream to one
     * that is backed by disk. This is the point at which we realise that too
     * much data is being written to keep in memory, so we elect to switch to
     * disk-based storage.
     * 
     * @exception IOException
     *                if an error occurs.
     */
    @Override
    protected void thresholdReached() throws IOException {
        if (prefix != null) {
            outputFile = File.createTempFile(prefix, suffix, directory);
        }
        FileOutputStream fos = new FileOutputStream(outputFile);
        memoryOutputStream.writeTo(fos);
        currentOutputStream = fos;
        memoryOutputStream = null;
    }

    // --------------------------------------------------------- Public methods

    /**
     * Determines whether or not the data for this output stream has been
     * retained in memory.
     * 
     * @return <code>true</code> if the data is available in memory;
     *         <code>false</code> otherwise.
     */
    public boolean isInMemory() {
        return (!isThresholdExceeded());
    }

    /**
     * Returns the data for this output stream as an array of bytes, assuming
     * that the data has been retained in memory. If the data was written to
     * disk, this method returns <code>null</code>.
     * 
     * @return The data for this output stream, or <code>null</code> if no such
     *         data is available.
     */
    public byte[] getData() {
        if (memoryOutputStream != null) {
            return memoryOutputStream.toByteArray();
        }
        return null;
    }

    /**
     * Returns either the output file specified in the constructor or the
     * temporary file created or null.
     * <p>
     * If the constructor specifying the file is used then it returns that same
     * output file, even when threashold has not been reached.
     * <p>
     * If constructor specifying a temporary file prefix/suffix is used then the
     * temporary file created once the threashold is reached is returned If the
     * threshold was not reached then <code>null</code> is returned.
     * 
     * @return The file for this output stream, or <code>null</code> if no such
     *         file exists.
     */
    public File getFile() {
        return outputFile;
    }

    /**
     * Closes underlying output stream, and mark this as closed
     * 
     * @exception IOException
     *                if an error occurs.
     */
    @Override
    public void close() throws IOException {
        super.close();
        closed = true;
    }

    /**
     * Writes the data from this output stream to the specified output stream,
     * after it has been closed.
     * 
     * @param out
     *            output stream to write to.
     * @exception IOException
     *                if this stream is not yet closed or an error occurs.
     */
    public void writeTo(OutputStream out) throws IOException {
        // we may only need to check if this is closed if we are working with a
        // file
        // but we should force the habit of closing wether we are working with
        // a file or memory.
        if (!closed) {
            throw new IOException("Stream not closed");
        }

        if (isInMemory()) {
            memoryOutputStream.writeTo(out);
        } else {
            FileInputStream fis = new FileInputStream(outputFile);
            try {
                copy(fis, out);
            } finally {
                closeQuietly(fis);
            }
        }
    }
}
